I have recently noticed a "ping" sound which is very noticable when sitting at drive throughs, I would imagine from the echo effect. It seems to be coming form the driver's-exhaust area, but is sporadic. It goes away when the car is in park and gets worse with engine rev. Of possible note, I have aftermarket Fab exhaust installed. Anyone heard of this one?

 

Could be bad gas. Did you fill up with a lower octane?

 

Nope- I always use premium and this problem has persisted much longer than one tankful